Host‐Dopant Interaction between Organic Thermally Activated Delayed Fluorescence Emitter and Host Material: Insight into the Excited State

Abstract Organic light‐emitting diodes (OLEDs) represent one of the most promising technologies for future displays and lighting sources, which have received extensive research attention. Purely organic thermally activated delayed fluorescence (TADF) emitters offer obvious advantages, including high efficiencies and low costs, and they are typically doped in host materials to achieve optimal device efficiencies. TADF emitters typically feature intramolecular charge transfer characteristics, and their excited states properties are sensitive to local environment, giving the implication that host materials can finely tune their emission properties. In recent years, the development of TADF emitters has been vigorous with abundant and fast‐growing reports on new design concepts and molecular structures. Comparatively, research on the host materials for TADF OLEDs has lagged, and reports on host materials, especially those providing insights into host‐dopant interactions are limited. This subject is at the interface of synthetic chemistry, physical chemistry, solid‐state physics, and computational modeling, etc. In this review article, current basic understanding of TADF and the reports on the impact of host materials on the photophysical properties/device performance of TADF emitters are reviewed to provide insights into the host‐dopant interactions, aiming to draw the attention of the research community from optoelectronics toward developing highly efficient TADF OLEDs.